If you walk for only about 16 hours per day, taking breaks to eat and sleep, it takes 3/2 more time, about 1,396,000,000 years.

Currently the average human lifespan in a post-industrial country is something like 82 years. The journey would take over 17 million lifetimes. Take every person in Tokyo and New York City and live each one of their lives one after the other, walking every day of their (your) lives. They (you) will have walked far enough to reach Proxima Centauri.